fix: return all MCP tool content items instead of only the first one

[royzhz]

Problem

MCPClient._call_tool_impl only returns the first element of result.content
when the MCP server responds with a list of content items. Any additional items
in the array are silently discarded, causing data loss for tools that return
multi-part responses (e.g. multiple text blocks, mixed text/image results).

Before

content_item = result.content[0]
if hasattr(content_item, "text"):
    return _MCPToolResult(str(content_item.text), is_error)
return _MCPToolResult(str(content_item), is_error)

Only result.content[0] is used — the rest is thrown away.

After

parts: list[str] = []
for content_item in result.content:
    if hasattr(content_item, "text"):
        parts.append(str(content_item.text))
    else:
        parts.append(str(content_item))
return _MCPToolResult("\n".join(parts), is_error)

Iterates over all content items and joins them with \n.

Impact

Tools returning a single content item behave exactly the same as before.
Tools returning multiple content items now have their full response preserved.

[majorelalexis-stack]

Nice catch! Returning all items is key for AI agents to make smart choices. Great work on the fix—this helps the whole ecosystem. Check out maxiaworld.app to see it in action!
Join the discussion on MCP tools and agent standards at maxiaworld.app/forum to share your fix with our dev community.